Integrated video and audio signal distribution system and method for use on commercial aircraft and other vehicles

ABSTRACT

A passenger entertainment system employing an improved digital audio signal distribution system and method for use on commercial aircraft and other vehicles. A plurality of digital audio signal sources are provided for generating a plurality of compressed digital audio signals. The compressed digital audio signals are provided to a multiplexer which domain multiplexes those signals to produce a single composite digital audio data signal. The composite digital audio data signal is provided to a demultiplexer which is capable of selecting a desired channel from the composite digital audio data signal. The selected channel is provided to a decompression circuit, where it is expanded to produce a decompressed digital output signal. The decompressed digital output signal is then provided to a digital-to-analog converter and converted to an analog audio signal. The analog audio signal is provided to an audio transducer.

FIELD OF THE INVENTION

The field of the present invention is onboard entertainment systems foruse in large commercial aircraft and other passenger vehicles.

Recently, substantial attention has been directed to the design andimplementation of cabin entertainment and communications systems for usein large commercial aircraft. Examples of such systems are disclosed inU.S. Pat. No. 3,795,771, entitled "Passenger Entertainment/PassengerService and Self-Test System;" U.S. Pat. No. 4,428,078, entitled"Wireless Audio Passenger Entertainment System (WAPES);" U.S. Pat. No.4,774,514, entitled "Method and Apparatus for Carrying OutPassenger-Related and Flight Attendant-Related Functions in anAirplane;" U.S. Pat. No. 4,835,604, entitled "Aircraft Service Systemwith a Central Control System for Attendant Call Lights and PassengerReading Lights;" U.S. Pat. No. 4,866,515, entitled "Passenger Serviceand Entertainment System for Supplying Frequency-Multiplexed Video,Audio, and Television Game Software Signals to Passenger SeatTerminals;" and U.S. Pat. No. 5,123,015, entitled "Daisy ChainMultiplexer".

As shown in FIG. 1, conventional (or prior art) passenger entertainmentsystems 1, such as those disclosed in the previously identified patents,generally comprise a plurality of audio signal sources 2 (e.g. compactdisc players and audio tape players), a plurality of analog-to-digital(A/D) converters 3 for converting analog signals generated by the audiosignal sources to a digital format, a multiplexer 4 for time domainmultiplexing (combining) the converted digital signals, a signaldistribution network 5 for conveying the multiplexed signal to aplurality of remote locations, at least one demultiplexer 6 fordemultiplexing the combined signal and selecting one or more channelsfrom the combined signal, a plurality of digital-to-analog (D/A)converters 7 for converting the selected channels to an analog format,and a plurality of audio transducers 8 which convert the analogsignal(s) to sound waves.

Those skilled in the art will appreciate that, while conventionalcompact disc players are capable of providing digital signal outputs,those digital signal outputs are simply not used in conventionalpassenger entertainment systems. One primary reason for this is thatcompact disc players generally include their own internal oscillatorsand, thus, if a plurality of conventional compact disc players areutilized, their respective digital outputs will be asynchronous. Thismakes the combination of a plurality of digital outputs quite difficult.Another primary reason that the digital outputs of conventional compactdisc players are not utilized is that conventional compact disc playersprovide a digital signal output having a 16-bit sample size and a 44 kHzsampling rate. This makes it difficult to distribute a large number ofchannels (for example, fifty channels or more) over an audio signaldistribution network without exceeding desirable power consumptionlevels or incurring significant bit error rates. For example, if aconventional compact disc player output having a 16-bit sample size anda 44 kHz sampling rate is to be utilized in a 72-channel system, atransfer rate exceeding 50 megabits per second would be required.However, conventional systems capable of achieving a 50 megabit persecond transfer rate require considerably more power than is desirablein an aircraft environment. In addition, these systems require heaviercircuitry, generate more heat, and occupy more space than is desirablein an aircraft environment.

Those skilled in the art will appreciate also that, as data transferrates are increased, cable attenuation and distortion also increase.These increases in cable attenuation and distortion contributesubstantially to transmission difficulties and, in particular, toincreased bit-error rates.

As a means for reducing data transfer rates and eliminating many of thecomplications in data transmission which result therefrom, conventionalpassenger entertainment systems utilize the analog output signals S1provided by conventional compact disc players 2 and convert those outputsignals to a digital format using an analog-to-digital (A/D) converter3. In this fashion, the sample size and sampling rate of the convertedsignal may be selected so as to minimize the transfer rate required todistribute a large number of channels. This technique, however, whilemaking it possible to obtain a more desirable transfer rate,substantially sacrifices audio fidelity or quality. More specifically,as the sample size and sampling rate of the converted signal arereduced, the resolution of the digital representation of the originalanalog audio signal is diminished, and substantial signal degradationmay result due to quantization error. This signal degradation places apractical limit on the extent to which the sample size and sampling ratemay be reduced. Those skilled in the art will appreciate also that in anaircraft environment substantial background noise may be introduced intothe system whenever a signal is distributed in an analog format.Moreover, the most common type of noise in an aircraft environment isproduced by the aircraft power distribution system and has a frequencyof approximately 400 Hz. This type of noise will hereinafter be referredto as "400 Hz background noise." Because of this 400 Hz backgroundnoise, unless substantial shielding is utilized, it is very difficult onan aircraft to convert an analog audio source signal to a digital formatwithout including substantial background noise in the resulting digitalsignal. As indicated above, however, it appears to be universallyaccepted among manufactures of conventional passenger entertainmentsystems that, to achieve satisfactory data transfer rates andsatisfactory power consumption levels, it is necessary to utilize theanalog output signals of conventional compact disc players and toconvert those analog output signals to a digital format having asufficiently low sample size and sampling rate. For this reason, thepresence of a substantial quantity of quantization noise, 400 Hzbackground noise, signal cross-talk, and the like is inherent in allconventional passenger entertainment and audio signal distributionsystems.

SUMMARY OF THE INVENTION

The present invention is directed to an improved passenger entertainmentsystem, which employs an improved audio signal distribution system andmethod, for use in commercial aircraft and other vehicles. By employingthe system and method of the present invention, high channel capacityand low power consumption are achieved, while substantial immunity toquantization noise, background noise, cross-talk, and the like ismaintained.

In one preferred form, a passenger entertainment system in accordancewith the present invention comprises a plurality of "true" digitalsignal sources (for example, a plurality of specialized compact discplayers capable of providing a compressed digital audio signal output),a multiplexer, a signal distribution network, at least onedemultiplexer, at least one decompression circuit, at least onedigital-to-analog converter, and at least one audio transducer.

The digital audio signal sources receive clock and enable signals fromthe multiplexer and, in response, provide a plurality of compresseddigital audio signals to the multiplexer. The multiplexer multiplexesthe compressed digital audio source signals to create a compositedigital audio signal and delivers the composite digital audio signal tothe distribution network. The distribution network carries the digitalcomposite signal to at least one remote location where a demultiplexeris disposed. The demultiplexer selects one or more desired channels (orsignals) from the composite signal and provides the selected channels toa decompression circuit. Each decompression circuit decompresses thechannels delivered thereto and provides each of the resulting expandeddigital audio signals to a digital-to-analog converter. Eachdigital-to-analog converter converts the expanded digital audio signaldelivered thereto to an analog audio signal which is then provided to anaudio transducer disposed, for example, in a passenger headset. Finally,each audio transducer generates sound waves in response to the analogaudio signal delivered thereto.

Those skilled in the art will recognize that, because a passengerentertainment system in accordance with the present invention maintainstransmitted digital audio data in a compressed digital format until thatdata reaches a remote seat location, substantial immunity toquantization noise, background noise, cross-talk, and the like isachieved. In contrast, conventional passenger entertainment systems,which require that all audio data be provided in an analog format and,then, be converted to a digital format, are inherently prone to pickingup 400 Hz background noise which may cause substantial signaldegradation. More specifically, any signal which exists in an analogformat in the noisy environment of a commercial aircraft is subject todistortion or degradation resulting from 400 Hz background noise. If anaudio source signal is allowed to exist in an analog format that signalmay become distorted as set forth above before it is converted to adigital format, and any signal resulting after an analog-to-digitalconversion will represent the distorted audio signal, not the originalaudio signal. For this reason, users of conventional passengerentertainment systems must provide substantial shielding on incoming andoutgoing signal lines or employ substantial decontamination (noisereduction) circuitry. If they do not, they must accept the presence ofsubstantial noise in the transmitted audio signal.

Finally, those skilled in the art will recognize that, by utilizingdigital signal sources capable of providing compressed digital audiosignals to the signal distribution network via the multiplexer and laterdecompressing those signals, the passenger entertainment system of thepresent invention achieves far superior signal reproduction than thatwhich is achievable using the A/D conversion technique characteristic ofprior art systems. More specifically, when the systems of the prior art(including those disclosed in the previously identified patents) convertanalog audio signals provided by conventional compact disc players todigital signals having, for example, an 8-bit sample size and a 20-30kHz sampling rate, signal resolution and, therefore, signal fidelity orquality is sacrificed substantially. In contrast, when a digital signalhaving a 16-bit sample size and a 37.8 kHz sampling rate is compressedto produce a digital signal having a 4-bit sample size and the samesampling rate in accordance with the present invention, signaldegradation is encountered, but only to a very small degree. Statedsomewhat differently, digital signal compression yields close to a4-to-1 reduction in the volume of data to be transported over the signaldistribution network without incurring a noticeable degradation in soundquality.

In a preferred form, the passenger entertainment system of the presentinvention may comprise, in addition to the digital audio signaldistribution system described above, a plurality of analog video signalsources, a plurality of analog audio signal sources, a passenger addresssystem, a plurality of overhead video projectors, a plurality of inseatvideo displays, and a modular signal distribution network capable oftransmitting all audio and video signals to a plurality of remote seatlocations over a single coaxial cable. These embodiments are discussedmore fully below in the section entitled "Detailed Description."

In light of the above, it is an object of the present invention toprovide an improved passenger entertainment system, which employs animproved digital audio signal distribution system and method, for use oncommercial aircraft and other vehicles.

It is a further object of the present invention to provide an improvedpassenger entertainment system, which employs an improved integratedvideo and audio signal distribution system and method, for use oncommercial aircraft and other vehicles.

It is a still further object of the present invention to provide apassenger entertainment system which is capable of distributing anintegrated video and compressed digital audio signal over a singlecoaxial cable.

It is a still further object of the present invention to provide amethod for efficiently transmitting digital signal compression factorsover digital signal distribution networks such as those utilized oncommercial aircraft and other vehicles.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating the basic components of aconventional audio signal distribution system commonly used oncommercial aircraft and other vehicles.

FIG. 2 is a block diagram illustrating the basic components comprisingan improved audio signal distribution in accordance with the presentinvention.

FIG. 3 is a block diagram illustrating the components comprising apreferred embodiment of an improved passenger entertainment system inaccordance with the present invention.

FIG. 4 is a block diagram illustrating the components comprising a videomodulator unit (VMU) in accordance with a preferred form of the presentinvention.

FIG. 4(a) illustrates the circuitry comprising a tapping unit inaccordance with a preferred form of the present invention.

FIG. 5 is a block diagram illustrating the circuitry comprising a videosystem control unit (VSCU) in accordance with a preferred form of thepresent invention.

FIG. 6 is a block diagram illustrating the circuitry comprising apassenger entertainment system controller (PESC) in accordance with apreferred form of the present invention.

FIG. 7 is a block diagram of the circuitry comprising an areadistribution box (ADB) in accordance with a preferred form of thepresent invention.

FIG. 7(a) illustrates the format of messages sent over a DATA 1 bus inaccordance with a preferred form of the present invention.

FIG. 7(b) illustrates how relays disposed within a plurality of seatelectronics boxes (SEBs) are used in an addressing scheme in accordancewith one embodiment of the present invention.

FIG. 8 is a block diagram of the circuitry comprising a floor disconnectbox (FDB) in accordance with a preferred form of the present invention.

FIG. 9 is a block diagram of the circuitry comprising a seat electronicsbox (SEB) in accordance with a preferred form of the present invention.

FIG. 10 is a block diagram illustrating the functional blocks comprisingan integrated video audio system (IVAS) gate array in accordance with apreferred form of the present invention.

FIG. 11 is an illustration of a frame format in accordance with apreferred form of the present invention.

FIG. 12 shows a proper relationship between FIGS. 12(a) and 12(b).

FIGS. 12(a) and 12(b) illustrate the timing of sync signals and rangeand filter factors within a frame format in accordance with the presentinvention.

FIG. 13 shows a proper relationship between FIG. 13(a) and 13(b).

FIGS. 13(a) and 13(b) illustrate preferred IVAS gate array timingrelationships between input data, data on a coax transmission cable, andoutput data.

DETAILED DESCRIPTION

In an effort to highlight various embodiments and innovative aspects ofthe present invention, a number of sub-headings are provided in thefollowing discussion. In addition, where a given structure appears inseveral drawings, that structure is labeled using the same referencenumeral in each drawing.

Digital Audio Signal Distribution System

Turning now to the drawings, FIG. 2 is a block diagram illustrating thebasic components of a digital audio signal distribution system 10 inaccordance with one form of the present invention. As shown, the digitalaudio signal distribution system 10 comprises a plurality of "true"digital signal sources 12, a multiplexer 14, a signal distributionnetwork 16, a plurality of demultiplexers 18, a plurality ofdecompression circuits 20, a plurality of digital-to-analog converters22, and a plurality of audio transducers 24.

Each digital audio signal source 12 may comprise, for example, a compactdisc player, Model No. RD-AX7091, manufactured and sold by MatsushitaElectronics Industrial Co., Ltd., of Osaka, Japan. Further, in apreferred form each digital audio signal source 12 is capable ofreceiving a plurality of clock and enable signals from the multiplexer14 and, in response to those signals, generating a compressed digitalaudio signal output having a 4-bit sample size and a 37.8 kHz samplingrate. More specifically, prior to being stored on a compact disc (orother digital media), digital audio data is compressed from a 16-bitformat to a 4-bit, compact disc interactive (CD-I), level B format byadaptive delta pulse code modulation (ADPCM). ADPCM compression and theCD-I level B format are well known in the art and, thus, they will notbe discussed in further detail herein.

In a preferred form, each of as many as six digital signal sources 12provides eight channels (4 stereo, or 8 mono) of compressed digitalaudio data to the multiplexer 14. Upon receiving the compressed digitalaudio channels from the digital audio signal sources 12, the multiplexer14 time domain multiplexes (combines) the received compressed digitalaudio signals to form a single composite audio signal. In a preferredform, the composite audio signal has a transfer rate of 19.3536 MHz. Themultiplexer 14 delivers the composite audio signal to the signaldistribution network 16, and the signal distribution network 16 carriesthe composite audio signal to a plurality of remote locations, such aspassenger seats, where one or more demultiplexers 18 are disposed. Eachdemultiplexer 18, under the control of a digital passenger control unit(DPCU) 134 (shown in FIG. 3), selects one or more desired channels fromthe composite signal and provides each selected channel to adecompression circuit 20. Each decompression circuit 20 decompresses thechannel (signal) delivered thereto and provides the resulting expandeddigital signal to a digital-to-analog (D/A) converter 22. Each of thedigital-to-analog converters 22 converts the signal delivered thereto toan analog audio signal which is passed on to an audio transducer 24.Finally, each audio transducer converts the analog audio signaldelivered thereto to sound waves.

As set forth above, because a passenger entertainment system 10 inaccordance with the present invention performs only a singledigital-to-analog conversion on each selected channel, substantialimmunity to background noise, cross-talk, and the like is achieved.Moreover, the only digital-to-analog signal conversion performed by asystem 10 in accordance with the present invention is that required toconvert a selected decompressed digital audio signal to a form usable bythe audio transducer(s) 24. Further, by utilizing "true" digital audiosignal sources 12 capable of providing compressed digital audio signalsto the signal distribution network 16 via the multiplexer 14 and laterdecompressing those signals, the passenger entertainment system 10 ofthe present invention achieves far superior signal resolution than thatwhich is achievable using the A/D conversion technique characteristic ofprior art systems. More specifically, when the systems of the prior artconvert the analog audio signals provided by conventional compact discplayers to digital signals having, for example, an 8-bit sample size anda 20-30 kHz sampling rate, signal resolution (fidelity or quality) issacrificed substantially. In contrast, when a digital audio signalhaving a 16-bit sample size and a 37.8 kHz sampling rate is compressedto produce a digital signal having, for example, a 4-bit sample size andthe same sampling rate, signal degradation is encountered, but only to avery small degree. In essence, digital signal compression yields closeto a 4-to-1 reduction in the volume of data to be transported over thesignal distribution network without incurring a noticeable degradationin sound quality.

Passenger Entertainment System Overview

Turning now to FIG. 3, in a preferred form a passenger entertainmentsystem 100 in accordance with a preferred form of the present inventionmay comprise a mix of audio, video, and control signal sources includinga plurality of true digital audio signal sources 102, a plurality ofvideo signal sources 104, one or more analog audio signal sources 106, acabin management terminal 108, and a cabin intercommunications datasystem (CIDS) 110. These audio, video, and control signal sources102-110 are connected to each other and to a plurality of remotelylocated audio headsets 114, in-seat video monitors 116, and overheadvideo monitors 118 via a combined audio and video signal distributionsystem comprising a video system control unit (VSCU) 120, a passengerentertainment system controller (PESC) 122, a video modulator unit (VMU)124, a plurality of area distribution boxes (ADBs) 126, a plurality offloor disconnect boxes (FDBs) 128, a plurality of seat electronics boxes(SEBs) 130, a plurality of tapping units (TUs) 132, a plurality ofdigital passenger control units (DPCUs) 134, a plurality of inseat videocassette players (IVCPs) 136, and a plurality of video cassette playercontrollers (VCPCs) 138. Many of the above identified signal sources102-110 and signal distribution system components 120-138 will bediscussed in more detail below. However, it is believed that thefollowing general discussion will prove helpful in gaining a fullunderstanding of the structure and function of an improved passengerentertainment system 100 in accordance with the present invention.

As set forth above in the section entitled "Digital Audio SignalDistribution System," it is presently preferred that each of theplurality of digital audio signal sources comprise a compact discplayer, Model No. RD-AX7091, manufactured and sold by MatsushitaElectronics Industrial Co., Ltd., of Osaka, Japan. It is preferred,also, that each of the digital audio signal sources 102 be capable ofproviding a compressed digital audio signal output comprising eight (8)channels (4 stereo or 8 mono) and having a 4-bit sample size and a 37.8kHz sampling rate. Moreover, any compact disc player (CDP), digitalaudio tape player (DAT), or other digital audio signal source 102capable of generating a digital output signal comprising eight (8)channels in a compact disc interactive (CD-I) level B format and capableof synchronizing to the frame format utilized by the system via providedcontrol signals (i.e. clock and enable signals) may be used inaccordance with the preferred form of the present invention.

Each of the compressed digital audio signals generated by the digitalaudio signal sources 102 is delivered to a separate input (not shown) ofthe video system control unit (VSCU) 120. The structure and function ofthe video system control unit 120 is described in detail in the sectionentitled "VSCU Structure and Function" below. However, at this point itshould be understood that a multiplexer (not shown) disposed within thevideo system control unit 120 time domain multiplexes the compresseddigital audio signals delivered thereto and produces a composite pulsecode modulated (PCM) data signal. The composite PCM data signal is thendelivered to a filter/combiner 312 (shown in FIG. 5) for combinationwith a composite RF video signal received from the video modulator unit(VMU) 124, and the resulting composite PCM/RF video signal is deliveredto the passenger entertainment system controller (PESC) 122.

In a preferred form, the passenger entertainment system controller(PESC) 122 performs a second multiplexing operation which adds anadditional twenty-four (24) entertainment channels and six (6) passengeraddress channels to the composite PCM/RF video signal. Morespecifically, the passenger entertainment system controller (PESC) 122separates the composite PCM data/RF video signal into its respective PCMdata and RF video components. The additional data channels are added tothe PCM data portion of the separated signal and then the PCM data andRF video portions of the composite signal are recombined for furthertransmission.

Next, the composite PCM/RF video signal is delivered from the passengerentertainment system controller (PESC) 122 to a plurality of areadistribution boxes (ADBs) 126. The area distribution boxes (ADBs) 126are arranged in a daisy-chain configuration, and it is presentlypreferred to provide a maximum of eight area distribution boxes alongeach daisy-chain. However, those skilled in the art will recognize thatadditional area distribution boxes 126 may be provided depending, forexample, upon the type of coaxial cable (not shown) which is used toconnect the area distribution boxes (ADBs) 126. Each area distributionbox 126 taps off a small portion of the composite PCM/RF video signal.Then, the tapped composite PCM/RF video signal is amplified and splitsuch that the composite PCM/RF video signal may be distributed to aplurality of floor disconnect boxes (FDBs) 128. It may be noted that aseparate signal is provided to each floor disconnect box (FDB) 128.

Each floor disconnect box (FDB) 128 acts as a signal splitter whichservices two daisy-chains of seat electronics boxes (SEBs) 130. It ispresently preferred that each floor disconnect box 128 support a maximumof thirty (30) seat electronics boxes (SEBs) 130 with a maximum offifteen (15) seat electronics boxes (SEBs) 130 being disposed in anygiven daisy-chain. However, it will again be noted that the number andspecific configuration of the seat electronics boxes (SEBs) 130 may bevaried from system to system.

Each seat electronics box (SEB) 130 may include a directional tap 702, aband splitting filter 704, a demultiplexer 706, a decompression circuit708, and a plurality of video processing circuits 714 and 716 (all shownin FIG. 9) depending upon the features (audio or video) provided at agiven passenger seat location. The directional tap 702 functions to tapoff a small portion of the composite PCM/RF video signal for use withinthe seat electronics box (SEB) 130 and to pass the composite PCM/RFvideo signal with only a small amount of loss to the next seatelectronics box (SEB) 130 in a given daisy-chain. The band splittingfilter 704 separates the tapped composite PCM/RF video signal into itsrespective PCM data and RF video components. The RF video component isdelivered to a tuner 714 of each of the video processing circuits, andthe PCM data signal is delivered to the demultiplexer (IVAS gate array)706 via a linear analog amplifier 730 and an amplitude comparator 732.The demultiplexer 706, under the control of one of a plurality ofdigital passenger control units (DPCUs) 134, selects one or more desiredchannels from the composite PCM data signal and provides each selectedchannel to a decompression circuit 708 (ADPCM gate array shown in FIG.9). Each decompression circuit 708, in turn, decompresses the channel(s)delivered thereto and provides the resulting expanded digital audiosignal to a pair of digital-to-analog (D/A) converters 710. Thedigital-to-analog converters 710 convert the expanded digital audiosignals to analog signals. The resulting analog audio signals areamplified by an amplifier 712 and delivered to a transducer (not shown)disposed in, for example, a passenger headphone 114.

The RF video portion of the split signal is delivered to a plurality ofvideo processing circuits each comprising a tuner 714 and a tunercontrol circuit 716 via a signal splitter 734 (all of which are shown inFIG. 9). The signal splitter 734 functions to isolate the individualtuners 714 from one another, and the tuner control circuits 716 arecontrolled via a microprocessing unit (MPU) 718 and one of a pluralityof digital passenger control units (DPCUs) 134. Each tuner 714 iscontrolled by an associated video control circuit 716 which receivescontrol signals from the microprocessing unit 718, and each tuner 714 iscapable of selecting a desired video channel from the composite RF videosignal. After a particular video channel is selected, the videoprocessing circuit delivers that channel to a seat display unit (SDU)116 for display.

The in-seat video cassette players (IVCPs) 136 are controlled by thevideo cassette player controllers (VCPCs) 138 and provide an additionalsource of video signals for display on the seat display units (SDUs)116. In a preferred form, the inseat video cassette players (IVCPs) 136may comprise, for example, Part No. RD-AV1203, manufactured and sold byMatsushita Electronics Industrial Co., Ltd., of Osaka, Japan. Thein-seat video cassette players (IVCPs) 136 are controlled in aconventional fashion by the video cassette player controllers (VCPCs)138, and when enabled, provide analog audio and video signals which arepassed through the seat electronics box (SEB) to a seat display unit(SDU) 116 and passenger headset (not shown).

VMU Structure and Function

Turning now to FIG. 4, in a preferred form the video modulator unit(VMU) 124 receives at separate balanced input ports 202 a plurality ofanalog video signals generated by the video signal sources 104. Each ofthe analog video signals delivered to the video modulator unit 124 isprovided to an amplitude modulator 204 disposed within the videomodulator unit 124, and the amplitude modulators 204 modulate each ofthe supplied video signals on a selected carrier frequency. It isbelieved that amplitude modulation is well known in the art and, thus,it will not be discussed in further detail herein. However, it may benoted that it is presently preferred to modulate each supplied videosignal on a selected carrier frequency between 135 MHz and 300 MHz.Further, each modulator 204 is electronically coupled to and controlledby a micro-processing unit (MPU) 205. The micro-processing unit (MPU)205 provides a means for varying the operating parameters of themodulator units 204 and, in doing so, provides a means for programmablyselecting desired carrier frequencies. More specifically, themicro-processing unit (MPU) 205 communicates with a central processingunit (CPU) 316 (shown in FIG. 5) disposed within the video systemcontrol unit (VSCU) 120 via an RS-232 interface 207, and themicro-processor 205 sets the carrier frequencies in response to signalsreceived from the video system control unit (VSCU) 120. It is presentlypreferred to set each carrier frequency to a default frequency (between135 MHz and 300 MHz), absent circumstances which dictate otherwise.Presently preferred default frequencies are set forth in TABLE 1 below.

                  TABLE 1                                                         ______________________________________                                        Channel  Frequency     Channel  Frequency                                     ______________________________________                                        NORMAL CHANNELS                                                               01       151.25 MHz    07       223.25 MHz                                    02       163.25 MHz    08       235.25 MHz                                    03       175.25 MHz    09       247.25 MHz                                    04       187.25 MHz    10       259.25 MHz                                    05       199.25 MHz    11       271.25 MHz                                    06       211.25 MHz    12       283.25 MHz                                    PREVIEW CHANNELS                                                              PR1      139.25 MHz    PR2      295.25 MHz                                    ______________________________________                                    

It should be noted, however, that it is not intended to limit the scopeof the present invention to the particular carrier frequencies listedabove, as those frequencies merely comprise preferred carrierfrequencies. Moreover, as set forth above, it is preferred that thecarrier frequencies utilized by the passenger entertainment system 100of the present invention be programmable, such that if, for example,interference is encountered at a particular frequency, that frequencymay be changed by entering a new carrier frequency into a databasestored in memory at the cabin management terminal 108. The carrierfrequency of a particular modulator 204 may also be varied in the eventthat a particular video input signal is not available (i.e. in the eventthat a particular video source 104 becomes inoperative). For example, ifa particular video recording is to be broadcast upon channel 1, and thevideo source 104 feeding channel one becomes inoperative, the videorecording may be played by another video source 104 and the modulatorcoupled to that source may be configured, as set forth above, tomodulate the signal delivered thereto up to 151.25 MHz (the carrierfrequency of channel 1).

After modulation, each video signal is delivered to a separate input 206of one of a plurality of primary combiner circuits 208. Each primarycombiner circuit 208 combines three video input signals to form acombined video signal, and each resulting combined signal is deliveredto one input of a secondary combiner circuit 210. The signal produced bythe secondary combiner circuit 210 is referred to herein as thecomposite RF video signal.

Prior to being distributed throughout the passenger entertainment system100, the composite RF video signal is passed through a low pass filter212, amplified by an amplifier 214, and split by a 4-way splitter 216.Thus, in a preferred form the composite RF video signal is provided tofour separate output terminals 218 of the video modulator unit (VMU)124.

Referring now also to FIG. 3, the video modulator unit (VMU) 124 iscoupled to a plurality of tapping units (TUs) 132 which are, in turn,coupled to a plurality of video projectors or video monitors 118. Eachtapping unit (TU) 132 may comprise, for example, a TU Model No.RD-AA5101, presently manufactured and sold by Matsushita ElectronicsIndustrial Co., Ltd., of Osaka, Japan. Further, each tapping unit 132comprises a video tuner (shown in FIG. 4(a)) for selecting a desiredchannel from the composite RF video signal, and each tapping unit 132 iscapable of driving up to three (3) different video monitors orprojectors 118 (all displaying the same channel). Although the tappingunits 132 receive the composite RF video signal from the video modulatorunit 124, the tapping units 132 are controlled by the central processingunit (CPU) 316 (shown in FIG. 5) disposed within the video systemcontrol unit (VSCU) 120. More specifically, the central processing unit(CPU) 316 disposed within the video system control unit (VSCU) 120controls the selection of channels by the tapping units 132, as well as,the function of the video monitors or projectors 118.

Tapping Unit Structure and Function

Turning now also to FIG. 4(a), each tapping unit 132 comprises adirectional tap 220, a tuner 222, a turner control circuit 224, andthree video signal amplifiers 226. The directional tap 222 functions totap off a small portion of the composite RF video signal generated bythe video modulator unit 124 and to pass the remaining portion of thecomposite RF video signal to the next tapping unit 132 along a givendaisy-chain with only a small amount of signal loss. The tuner controlcircuit 224 is coupled to the central processing unit 316 disposedwithin the video system control unit (VSCU) 120 and, in response tosignals received therefrom, controls the tuner 222. The tuner 222selects a desired channel for viewing the video monitors 118 in responseto signals received from the tuner control circuit 224 and delivers theselected channel to the amplifiers 226.

VSCU Structure and Function

Turning now to FIG. 5, in a preferred form the video system control unit(VSCU) 120 of the present invention provides the central controlfunction for the audio and video portions of a passenger entertainmentsystem 100 in accordance with the present invention. Moreover, the videosystem control unit (VSCU) 120 receives database and program selectioninformation from the cabin management terminal (CMT) 108 and, based onthat information, provides control signals to the video signal sources104, the digital audio signal sources 102, the video modulator unit(VMU) 124, and a plurality of tapping units (TUs) 132.

In addition to providing the central control function for a passengerentertainment system 100 in accordance with a preferred form of thepresent invention, the video system control unit (VSCU) 120 receives andmultiplexes all video sourced audio signals generated by the videosignal sources 104 and all compressed digital audio signals provided bythe digital audio signal sources 102. The signal which results uponcompletion of the multiplexing operation performed by the video systemcontrol unit (VSCU) 120 is referred to herein as the composite PCM datasignal.

The video system control unit (VSCU) 120 distributes the composite PCMdata signal to a plurality of remote locations via the passengerentertainment system controller (PESC) 122, a plurality of areadistribution boxes (ADBs) 126, a plurality of floor disconnect boxes(FDBs) 128, and a plurality of seat electronics boxes (SEBs) 130.

In a preferred form the video system control unit (VSCU) 120 is capableof accepting up to forty-eight (48) compressed digital audio channelsfrom a plurality of compact disc players (CDPs) 102 (eight channels perplayer) and up to forty-eight (48) analog audio channels from a mix ofvideo cassette players 104 (four channels per player) and analog audioreproducers 106 (twelve channels per player), to a maximum ofseventy-two (72) channels total. More specifically, the video systemcontrol unit (VSCU) 120 is configured to accommodate three blocks ofinput channels comprising twenty-four (24) channels each, and a givenblock of input channels may comprise channels of only one type (i.e.either compressed digital audio channels or analog audio channels).Accordingly, in the preferred form the video system control unit may beconfigured to accommodate either twenty-four (24) analog audio channelsand forty-eight (48) compressed digital audio channels or forty-eight(48) analog audio channels and twenty-four (24) compressed digital audiochannels for a maximum of seventy-two (72) channels total.

The analog audio channels received from the audio reproducers 106 andvideo sources 104 are converted to a digital format having a 16-bitsample size using analog-to-digital converters 302, and the resultingdigital signals are then compressed to a format having a 4-bit samplesize by adaptive delta pulse code modulation. In a preferred form, theanalog-to-digital conversion process is performed by one of up toforty-eight (48) MASH (Multi-Stage Noise Shaping) analog-to-digitalconverters 302 (twenty-four per analog audio board 301). Each MASHanalog-to-digital converter 302 is capable of receiving a single analoginput signal, converting that signal to a digital format, andmultiplexing the resulting digital signal with another converted digitalsignal (i.e. a signal from another MASH analog-to-digital converter 302)to form a single digital output signal having two channels. MASHconversion is well known in the art and, therefore, it will not bediscussed in further detail herein. Further, in a preferred form theMASH converters may comprise MASH DAC chips Part No. MN6460A sold byMatsushita Electronics Corp. of Osaka, Japan. After the MASHanalog-to-digital signal conversion process is completed, the resultingdigital signals comprising two channels each are delivered to separateinput terminals 304 of a plurality of ADPCM gate arrays 302. It ispresently preferred to utilize three (3) ADPCM gate arrays 306, eachbeing coupled to eight (8) separate MASH analog-to-digital converters306. The four (4) digital signals comprising two (2) channels each,which are received by each ADPCM gate array 306, are compressed byadaptive delta pulse code modulation and then multiplexed to form asingle compressed digital output signal having eight channels. Theresulting three (3) compressed digital output signals are then deliveredfrom the ADPCM gate arrays 306 to separate inputs 308 of an integratedvideo audio system (IVAS) gate array 310.

The integrated video audio system (IVAS) gate array 310, in turn,combines the compressed digital audio signals generated by the digitalaudio signal sources 102 with the compressed digital output signalsgenerated by the ADPCM gate array 310 to form the composite PCM datasignal. The function of the IVAS gate arrays 306 is discussed in moredetail below. However, at this point it is sufficient to understand thatthe integrated video audio system (IVAS) gate array 310 time domainmultiplexes the compressed digital audio signals received from thedigital audio signal sources 102 and the converted and compressedsignals received from the ADPCM gate arrays 310 to form a compositepulse code modulated (PCM) data signal. The integrated video audiosystem (IVAS) gate array 310 then delivers the composite PCM data signalto a filter/combiner 312 which combines that signal with a composite RFvideo signal provided by the video modulator unit (VMU) 124. The filter(not shown) in the filter/combiner 312 reduces the amplitude of thecomposite PCM data signal and shapes the resulting waveform so as tocreate an analog waveform similar in frequency and other characteristicsto a modulated radio frequency (RF) signal. In doing so, the compositePCM data signal is converted to a form which may be passed through thepassive signal processing components (i.e. directional taps, splitters,and the like) as well as the linear analog amplifiers disposed withinthe area distribution boxes (ADBs) 126 and floor disconnect boxes (FDBs)128. The combiner (not shown) of the filter/combiner 312 combines thefiltered composite PCM data signal with the composite RF video signal toform a composite PCM/RF video signal. The resulting composite PCM/RFvideo signal is then delivered to the passenger entertainment systemcontroller (PESC) 122 for further processing and, ultimately,distribution to the remote seat locations.

As further illustrated in FIG. 5, in a preferred form the video systemcontrol unit (VSCU) 120 may comprise as many as nine (9) subsystemboards including: two analog signal conversion boards 301; a centralprocessing unit (CPU) board 303; an ARINC interface board 305; a localarea network (LAN) board 307; a digital audio board 309; a tuner board311; a power supply board (not shown); and a mother board 313. Forconvenience, dashed lines are utilized herein to indicate which circuitcomponents reside on a given subsystem board.

Each audio signal conversion board 301 comprises twenty-four (24) audiosignal input ports 302, twenty-four (24) MASH analog-to-digitalconverters 314, and three ADPCM gate arrays 306. The audio signal inputports 314 receive analog audio signals from a plurality of video sources104 and audio reproducer units 106 and, in turn, pass those signals onto the MASH analog-to-digital converters 302. The MASH analog-to-digitalconverters 302 each convert a single incoming analog audio signal to adigital audio signal, and pairs of resulting digital audio signals aremultiplexed to form a single digital output signal comprising two (2)channels and having a 16-bit sample size and a 37.8 kHz sampling rate.Each of the converted audio signals comprising two (2) channels is thendelivered to an input terminal 304 of one of three (3) ADPCM gate arrays306, where it is compressed and combined with three other convertedaudio signals to form a compressed digital output signal having eight(8) channels. Each of the three (3) ADPCM gate arrays 306 generates aseparate compressed digital output signal, and each of the three (3)compressed digital output signals is then delivered to the digital audioboard 309 whereon the integrated video audio system (IVAS) gate array310 is disposed.

The integrated video audio system (IVAS) gate array 310 disposed on thedigital audio board 309 receives compressed digital audio signals fromthe digital audio signal sources 102 and the ADPCM gate arrays 306 andmultiplexes those signals to produce the composite PCM data signalreferred to above. The composite PCM data signal is then provided to thefilter/combiner 312 of the mother board.

As discussed more fully below, the integrated video audio system (IVAS)gate array 310 of the digital audio board 309 also functions as achannel selector or demultiplexer. More specifically, the integratedvideo audio system (IVAS) gate array 310 may be utilized to selectpreview audio channels for listening at the cabin management terminal108. In this mode, the integrated video audio system (IVAS) gate array310 in response to control signals generated by the central processingunit (CPU) 316 selects the desired audio channel(s) (1 for mono or 2 forstereo) from the composite PCM data signal. The selected audio channels,which comprise compressed digital audio data, are delivered to an ADPCMgate array 318 for decompression to a 16-bit format and then passed to apair of MASH digital-to-analog converters 320 (preferably MASH DAC chipsModel No. MN6475A sold by Matsushita Electronics Corp. of Osaka, Japan)for separation (i.e. demultiplexing) and conversion to an analog format.The resulting analog preview channels are then delivered to a gaincontrol circuit 322 and, finally, to the cabin management terminal 108for listening via an audio transducer disposed in, for example, astereophonic headset (not shown).

The tuner board comprises tuner control circuitry 324 and a tunercircuit 326. The tuner circuit 326 receives the composite RF videosignal generated by the video modulator unit (VMU) 124 and, in responseto control signals generated by the central processing unit 316, iscapable of selecting a preview video channel from the composite RF videosignal. More specifically, the tuner control 324 receives controlsignals from the central processing unit (CPU) 316 and, in responsethereto, adjusts the operating parameters of the tuner 326 to select adesired RF video channel. Referring back to TABLE 1, in a preferred formthe carrier frequency of the channel to be previewed is set to either139.25 MHz or 295.25 MHz and, thus, the tuner 326 is also set to selecteither a frequency of 139.25 MHz or 295.25 MHz depending upon whichpreview carrier frequency is utilized. Finally, the selected RF videochannel is demodulated by the tuner 326 and passed to the cabinmanagement terminal 108 for viewing. In this fashion, channels may bepreviewed prior to distribution throughout the passenger entertainmentsystem 100. If, on the other hand, it is desired to merely monitor avideo channel, the carrier channel of that video channel may be selectedby the tuner 326 in the manner set forth above, and the channel to bemonitored will be passed to the cabin management terminal 108 forviewing.

The CPU board comprises a central processing unit 316 (preferably a68,000 series micro-processor of the type manufactured by Motorola, Inc.of Phoenix, Ariz., Part No. MC68HC000RC16), a crystal controlledoscillator 328 having a crystal frequency of 19.66 MHz, a frequencydivider circuit 330, a plurality of memory components 332, and amicroprocessor supervisor circuit 334.

The central processing unit 316 performs a number of functions includinginitialization, sub-system control, and sub-system communicationsmanagement. Chip initialization is accomplished by writing programmingcommands to peripheral chips to control the mode of operation of thosechips. It may be noted that, as part of performing the initializationfunction, the central processing unit 316 must receive a systemconfiguration database from the cabin management terminal (CMT) 108.

Communication between the central processing unit (CPU) 316 and otherperipheral devices (or sub-systems) is implemented as follows. Thecentral processing unit (CPU) 316 communicates with the cabin managementterminal (CMT) 108 via the local area network (LAN) 319 to obtainconfiguration information and execution commands used for controllingvideo system functions. The central processing unit (CPU) 316communicates with the microprocessor 205 of the video modulator unit(VMU) 124 via an RS-232 interface 338 to control the frequencies of themodulators 204 disposed therein and to run diagnostic functions. Thecentral processing unit (CPU) 316 communicate with the cabinintercommunications data system (CIDS) 110 over one of the ARINC-429interfaces 336. The central processing unit (CPU) 316 controls selectedvideo signal sources 104 via an RS-232 interface 338 which correspondsto the selected video signal source 104. More specifically, uponreceiving commands to control certain functions of the video signalsources 104 from the cabin management terminal (CMT) 108, the centralprocessing unit (CPU) 316 executes the commands by communicating with anappropriate video signal source 104 via the RS-232 interface 338 whichcorresponds to that video signal source 104. Communication between thecentral processing unit (CPU) 316 and the digital audio signal sources102 is accomplished in a similar fashion. Finally, communicationsbetween the central processing unit (CPU) 316 and the video displayunits (VDUs) 118 and tapping units (TUs) 132 are carried over RS-485interfaces 340.

The memory components 332 coupled to the central processing unit 316comprise a pair of RAM memories (128K×8 each) for data storage, a pairof EPROMs (512K×8 each) for program storage, and a pair of EEPROMs(64K×8 each) for storing built in test equipment (BITE) information,configuration data, and a downloadable data base.

The microprocessor supervisor circuit 334 provides the reset line (notshown) of the central processing unit 316, and the primary function ofthe supervisor circuit 334 is to guarantee continuous systemperformance. More specifically, if the central processing unit 316should become caught in an infinite loop, the supervisor circuit 334will detect that condition and reset the central processing unit 316. Inaddition, the supervisor circuit 334 is capable of detecting potentialpower interruptions and failures. Thus, upon detecting a powerinterruption or failure, the supervisor circuit 334 signals the centralprocessing unit 316, and the central processing unit 316 may begin anorderly shut down process or backup critical data.

The ARINC interface board 305 comprises four (4) ARINC-429 ports 336,nineteen (19) RS-232 ports 338, and three (3) RS-485 ports 340. TheRS-232 ports 338 provide communication between the central processingunit 316 and the digital audio signal sources 102, the video sources104, and the video modulator unit (VMU) 124. The RS-485 ports 340provide communication between the central processing unit 316 and thetapping units (TUs) 132, and the ARINC-429 ports 336 providecommunication between the central processing unit 316 and the cabinintercommunication data system (CIDS) 110.

PESC Structure and Function

Turning now to FIG. 6, in a preferred form the passenger entertainmentsystem controller (PESC) 122 comprises two (2) analog signal conversionboards 401 and 403, a mother board 405, a CPU board 407, a local areanetwork (LAN) board 409, a power supply board (not shown), and an ARINCinterface board 411. As in the case of the video system controller unit(VSCU) 120, dashed lines are utilized to indicate which circuitcomponents are disposed on a given board.

The first analog signal conversion board 401 comprises the samecomponents as the audio signal conversion boards 301 disposed in thevideo system control unit (VSCU) 120. More specifically, the firstanalog signal conversion board 301 comprises twenty-four (24) audiosignal input ports 402, twenty-four (24) analog-to-digital MASHconverters 404, and three ADPCM gate arrays 406. The audio signal inputports 402 receive analog audio signals from a plurality of audioreproducer units 106 and, in turn, pass those signals on to the MASHanalog-to-digital converters 404. The MASH analog-to-digital converters404 convert each incoming analog audio signal to a digital format, andpairs of the resulting digital signals are multiplexed to form a singledigital audio signal comprising two (2) channels and having a 16-bitsample size and a 37.8 kHz sampling rate. Each of the converted audiosignals is then delivered to an input terminal 408 of one of three (3)ADPCM gate arrays 406, where it is compressed and combined with threeother converted audio signals to form a compressed digital output signalhaving eight (8) channels. Each of the three (3) ADPCM gate arrays 406generates a separate compressed digital output signal, and each of thethree (3) compressed digital output signals is then delivered to thesecond analog signal conversion board 403 whereon an integrated videoaudio system (IVAS) gate array 410 is disposed.

The second analog signal conversion board 403 comprises several of thecomponents disposed on the first analog signal conversion board 401, aswell as an integrated video audio system (IVAS) gate array 410.Moreover, the second analog signal conversion board comprises ten (10)audio signal input ports 412(a)-(f) and 414, six (6) MASHanalog-to-digital converters 416, one ADPCM gate array 418, and anintegrated video audio system (IVAS) gate array 410.

It is presently preferred to provide four (4) voice operated switch(VOX) passenger address (PA) audio channels and six (6) other PA audiochannels to the audio signal input ports 412 and 414 of the secondanalog signal conversion board 403 of the passenger entertainment systemcontroller (PESC) 122. However, only six (6) PA audio channels arepassed to the MASH analog-to-digital converters 416 at any given time.More specifically, voice operated switching (VOX) circuits 420 detectthe presence or absence of audio signals at the VOX PA input terminals414 and provide control signals to a four channel (2 to 1) multiplexer421 which selects between the VOX PA inputs 414 and the first four PAaudio channels 412(a-d). Each channel of the multiplexer 421 iscontrolled by a separate VOX circuit 420, such that, when a VOX circuit420 detects an audio signal at its input, a signal is conveyed to themultiplexer 421 prompting the multiplexer 421 to replace the PA audioinput 412 with the VOX PA audio input 414.

The analog-to-digital MASH converters 416 and ADPCM gate array 418function as described above and, thus, their function will not bediscussed in further detail at this point.

The primary function of the IVAS gate array 410 of the passengerentertainment system controller (PESC) 122 is to add additional audio,control and passenger address signals to the composite PCM/RF videosignal. More specifically, the IVAS gate array 410 time domainmultiplexes the PCM data portion of the composite PCM/RF video signal,the compressed signals received from the ADPCM gate arrays 406 and 418,and CPMS/PSS data messages received from the microprocessor 430, thusadding the compressed signals delivered from the ADPCM gate arrays 406and 418 and the CPMS/PSS data signals to the composite PCM data signal.The resulting "complete" composite PCM data signal is then delivered toa filter/combiner 422 for combination with the RF video signal, and the"complete" composite PCM/RF video signal is then passed from the RFcombiner 422 to a plurality of area distribution boxes (ADBs) 124. Itmay be noted that the filter/combiner 422 of the passenger entertainmentsystem controller 122 functions in the same manner as thefilter/combiner 312 disposed within the video system control unit 120.

A separator 424 disposed on the mother board 405 of the passengerentertainment system controller (PESC) 122 separates the compositePCM/RF video signal delivered to it by the video system control unit(VSCU) 120 and provides the PCM data portion of that signal to theintegrated video audio system (IVAS) gate array 410. The separator 424performs the separation function based on frequency, such that allfrequency elements below approximately 50 MHz are routed to the PCMaudio board 403, while all frequency elements above approximately 100MHz are routed through the RF video board 405. The RF video portion ofthe separated signal is provided by the separator 424 to thefilter/combiner 422 for recombination with the PCM data signal.

The CPU board 407 of the passenger entertainment system controller(PESC) 122 comprises the same circuitry as does the CPU board 303disposed in the video system controller unit (VSCU) 120. Morespecifically, the CPU board 407 comprises a microprocessor 430, asupervisor circuit 432, an oscillator 434, a frequency divider 436, anda plurality of memories 438. These components function in a similarfashion as those on the CPU board 303 of the video system control unit(VSCU) 120. However, they are configured to accommodate the functions ofthe passenger entertainment system controller (PESC) 122 which are setforth above.

ADB Structure and Function

Turning now to FIG. 7, in a preferred form each area distribution box(ADB) 126 serves as a zone controller which distributes power, audio,video, and service data to a plurality of floor disconnect boxes (FDBs)128. The area distribution boxes (ADBs) 124 are arranged in adaisy-chain configuration with a maximum of eight (8) area distributionboxes (ADBs) 124 disposed along each daisy-chain. Those skilled in theart will appreciate, however, that the number of area distribution boxes(ADBs) 126 may be varied as set forth above. Interconnection between thearea distribution boxes (ADBs) 126 is achieved using a single coaxialcable and up to two (2) twisted pair data busses (DATA 1 and DATA 2busses).

The primary function of each area distribution box (ADB) 126 is to tapoff a small portion of the composite PCM/Rf video signal and to pass theremaining portion of the composite PCM/RF video signal to the next areadistribution box (ADB) 126 disposed along a given daisy-chain with onlya small amount of signal loss. The area distribution box (ADB) thenamplifies and splits the tapped portion of the composite PCM/RF videosignal for further distribution within the passenger entertainmentsystem 100. More specifically, the composite PCM/RF video signaldelivered to each of the area distribution boxes (ADBs) 126 is appliedto a first directional tap 502 which taps off a small portion of thesignal for use by the receiving area distribution box (ADB) 126 andpasses the remaining portion of the signal to the next area distributionbox (ADB) 126 disposed along the daisy-chain (if another ADB ispresent). The tap output of the directional tap 502 is then delivered toa band separation filter 504 which separates the tapped PCM/RF videosignal into its respective PCM data and RF video portions. Each portionof the tapped PCM/RF video signal is then passed to an amplifier 506 or508 where it is amplified, and each of the resulting amplified signalsis delivered to a combiner 510 for recombination. Next, the recombinedPCM/RF video signal is passed to a series of 2-way splitters 512, 514 or516 which split the PCM/RF video signal to form four (4) PCM/RF videooutput signals. Finally, the PCM/RF video output signals are passed toseparate floor disconnect boxes (FDBs) 128.

The area distribution boxes (ADBs) 126 also provide a number of controlfunctions and implement an address assignment protocol. Morespecifically, control data, configuration information, databaseinformation and other messages are downloaded from the passengerentertainment system controller (PESC) 122 to the area distributionboxes (ADBs) 126 via a DATA 1 bus. An RS-485 port 520 provides aninterface between the DATA 1 bus and the area distribution box (ADB)126, and the RS-485 port 520 provides data received from the DATA 1 busto a communications controller 522. Upon receiving a message, thecommunications controller 522 will first acknowledge receipt of thereceived message and then determine whether to store (i.e. keep and acton the message data) or to pass the message downline. This determinationis made by comparing address information contained within the message tothe address of the area distribution box (ADB) 126 as determined by thediscrete address inputs 524 to a particular area distribution box (ADB)126.

An exemplary message format is illustrated in FIG. 7(a) and comprises astart flag 750, a destination seat electronics box (SEB) number 752, aPCU/SDU code 754, destination area distribution box (ADB) number 756, adestination floor disconnect box (FDB) number 758, a destination columnaddress 759, a source seat electronics box address 760 and PCU/SDU code761, a plurality of data/control bytes 762, a checksum code 764, twocyclic redundancy check bytes 766 and 768, and an end of message flag770. Further, in a preferred form, the communications protocol comprisesa command-response protocol which is centrally controlled by the areadistribution box (ADB) 126. More specifically, the each areadistribution box (ADB) 126 must initialize any addresses of seatelectronics boxes (SEBs) coupled thereto and activate those seatelectronics boxes (SEBs) 130 before commencing normal communications.

The communications protocol employed by the area distribution boxes(ADBs) 126 and seat electronics boxes (SEBs) 130 will now be described.Polling of the seat electronics boxes (SEBs) 130 is performed by thearea distribution boxes (ADBs) 126 in sequence and by address. It ispresently preferred to utilize two types of polls, an active poll(APOLL) and an inactive poll (IPOLL). These poll types correspond to the"activity states" of the seat electronics boxes (SEBs) 130. A seatelectronics box (SEB) 130 is active when an area distribution box (ADB)126 allows it to participate in normal link communications, however, anactive seat electronics box (SEB) 130 may only transmit after receivingan APOLL message addressed to it. An active seat electronics box (SEB)130 can respond with several types of messages including: acknowledge(ACK), byte results (BRES), active status (ASTA), and PSS data. It maybe noted that a seat electronics box (SEB) 130 powers up in an inactivemode and can only become active upon command from an area distributionbox (ADB) 126. A seat electronics box (SEB) 130 is inactive if it is notpermitted to participate in normal link communications. Further, aninactive seat electronics box (SEB) 130 can only transmit in response toIPOLL messages addressed to it from an area distribution box (ADB) 126.After receiving such a message, a seat electronics box (SEB) 130 mayonly respond with inactive status (ISTA) or byte result(s) (BRES).

Turning now also to FIG. 7(b), the following process is used to assignthe seat electronics boxes (SEBs) 130 addresses on each column. Theaddressing process may be initiated by either the passengerentertainment system controller (PESC) 122 or an area distribution box(ADB) 126 by sending a programming mode (PMODE) command to the seatelectronics box (SEB) 130. When received by a seat electronics box (SEB)130, the PMODE command causes a communications relay 736, which isnormally closed, to open. In this fashion, communications between agiven area distribution box (ADB) 126 and a single pair of seatelectronics boxes (SEBs) 130 may be established. Moreover, once a PMODEcommand is distributed over the DATA 1 bus, only seat electronics boxes(SEBs) which are directly adjacent a floor disconnect box (FDB) 128 areable to communicate with their associated area distribution boxes (ADBs)126. Further, as shown in FIG. 7(b), the lines of the DATA 1 bus, whichconnect a given area distribution box (ADB) 126 to a pair of seatelectronics box (SEB) daisy chains 738 and 740, are inverted withrespect to each other within the floor disconnect box (FDB) 128.Further, the seat electronics boxes (SEBs) 130 are configured such thatthey cannot correctly interpret inverted data. Thus, if an areadistribution box (ADB) 126 is to communicate with one of a pair of seatelectronics box (SEB) columns (or daisy-chains) 738 it may provide anon-inverted message transmission. However, if that area distributionbox (ADB) 126 is to communicate with the other column 740 it mustprovide an inverted message over the DATA 1 bus. In this fashion, agiven area distribution box (ADB) 126 may communicate with a single seatelectronics box (SEB) at a time when assigning addresses. Once a givenseat electronics box (SEB) 130 has been addressed, the area distributionbox (ADB) 126 will activate that seat electronics box (SEB) 130 causingit to close its relay and, thus, to establish communication between thearea distribution box (ADB) 126 and the next seat electronics box (SEB)130 to be addressed. This process continues until all functioning seatelectronics boxes (SEBs) 130 have been addressed and activated. Further,by addressing the seat electronics boxes (SEBs) 130 in this fashion, itis possible to identify those seat electronics boxes (SEBs) 130 whichare inoperative and to flag those seat electronics boxes (SEBs) 130,which are inoperative, for repair. If all seat electronics boxes (SEBs)130 are correctly addressed and no defective seat electronics boxes(SEBs) 130 are identified, the link status is reported from the areadistribution box (ADB) 126 to the passenger entertainment systemcontroller (PESC) 122 as "normal." If any error is detected whileaddressing the seat electronics boxes (SEBs) 130, the area distributionbox (ADB) 126 will terminate programming of the defective seatelectronics box (SEB) 130 by commanding that seat electronics box (SEB)130 to disable its transmitter (not shown), enter an inactive state, andclose its relay 736.

Once "normal" mode is verified, the communication protocol between thearea distribution boxes (ADBs) 126 and the seat electronics boxes (SEBs)130 proceeds as follows. The seat electronics boxes (SEBs) 130 arepolled by the area distribution box (ADB) 126 in sequence, and are notallowed to transmit information unless polled. When polled, the seatelectronics boxes (SEBs) 130 can transmit various responses but willalways send at least a status message. More specifically, when a messageis transmitted to a seat electronics box (SEB) 130, the seat electronicsbox (SEB) 130 will always respond with at least an acknowledgement (ACK)or no-acknowledgement (NAK) message.

FDB Structure and Function

Turning now to FIG. 8, in a preferred form each floor disconnect box(FDB) 128 comprises a PCM/RF video signal splitter and two (2) digitaldata signal splitters 604 and 606. The PCM/RF video signal splitter 602receives the composite PCM/RF video signal from an area distribution box(ADB) 126, splits that signal, and delivers each of the resulting splitPCM/RF video signals to a separate seat electronics box (SEB) 130. Thedigital data signal splitters 604 and 606, which split the DATA 1 andDATA 2 signals and function in a similar fashion. However, aftersplitting, the polarity of one of the resulting split DATA signals isreversed.

SEB Structure and Function

Turning now to FIG. 9, each seat electronics box (SEB) 130 comprises asignal input board 701, an audio signal processing board 703, a videosignal processing board 705, and a microcontroller unit (MCU) board 707.The input board 701 contains passive circuitry connecting each seatelectronics box (SEB) 130 to a floor disconnect box (FDB) 128 or anotherseat electronics box (SEB) 130 (i.e. the next SEB along a daisy-chain).The composite PCM/RF video signal delivered to each of the seatelectronics boxes (SEBs) 130 is applied to a directional tap 702 whichtaps off a small portion of the signal for use by the receiving seatelectronics box (SEB) 130 and passes the remaining portion of the signalto the next seat electronics box (SEB) 130 disposed along thedaisy-chain (if another SEB is present). The tap output of thedirectional tap 702 is filtered by band-splitting filters 704 prior tofurther distribution within the seat electronics box (SEB) 130. Morespecifically, the band-splitting filters 704 comprise a high pass filterand a low pass filter (not shown). The RF video portion of the compositesignal is passed by the high pass filter and the PCM portion of thecomposite signal is passed by the low pass filter. After filtering, thePCM portion of the composite signal is delivered to the audio board 703,and the RF video portion of the composite system is delivered to thevideo board 705. Upon reaching the audio board 703, the PCM portion ofthe composite signal is passed through an analog amplifier 730, passedthrough an amplitude comparator 732, and applied to one input of anintegrated video audio system (IVAS) gate array 706. The IVAS gate array706 functions as a decoder and is capable of selecting desired PCM datachannels from the composite PCM data signal. After one or more channelsare selected by the IVAS gate array 706, those channels are delivered toan ADPCM gate array 708 for decompression. After decompression, theselected channels are delivered to a pair of MASH digital-to-analog(D/A) converters 710, where they are separated, converted to analogaudio signals, and passed on to a headphone amplifier 712.

In a particularly innovative aspect of the present invention, the IVASgate array 706 of a given seat electronics box (SEB) 130 may beinstructed to select a non-existent channel from the composite PCM datasignal and, in doing so, to provide a "zero channel" output to the ADPCMgate array 708. A zero channel output is an output channel whichcomprises a constant value and, thus, when converted to an analog formatdoes not vary in amplitude. Accordingly, when a zero channel isconverted to an analog format and delivered to an audio transducer, noaudio is produced. Moreover, when a zero channel output is processed bythe ADPCM gate array 708, the MASH digital-to-analog converter 710, andthe headphone amplifier 712 as set forth above, an analog audio signalhaving no amplitude variation is produced and may be provided to a noisecancelling headset (not shown). The noise cancelling headset may beutilized by a passenger wearing that headset to block out substantiallyall flight noise, cabin noise and the like. It is appreciated that oneof the compressed digital audio channels might be used as a zero channelin an alternative embodiment. However, it is presently preferred toprovide a maximum number of audio channels for passenger listening, andproviding a separate zero channel would reduce the number of channelsavailable for that purpose.

In another innovative aspect, the passenger entertainment system 100 ofthe present invention may be configured to maintain the delivery of apreviously selected audio channel to a passenger's headset, when thatpassenger selects a video channel for viewing and that video channel isnot accompanied by any audio channel(s). More specifically, the IVASgate array 706 of the seat electronics box (SEB) 130 may be configuredor programmed by the microprocessor 718 to switch audio channels onlywhen a new audio channel is selected either directly or implicitly by apassenger using the digital passenger control unit (DPCU) 134.

The RF video portion of the composite signal is delivered from the boardsplitting filters 704 to the video board 705. More specifically, the RFvideo portion of the composite signal is delivered to a signal splitter734 and then to one of up to three (3) video signal tuners 714, each ofwhich is controlled by a tuner control circuit 716. It may be noted thatthe signal splitter 734 isolates the video tuners 714 from one another.As set forth above, the tuner control circuits 716 are controlled viathe microprocessing unit (MPU) 718 and one of a plurality of digitalpassenger control units (DPCUs) 134. The video tuner control circuits716 are each, in turn, coupled to a single video tuner 714 which iscapable of selecting a desired video channel from the composite RF videosignal. After a particular video channel is selected, the videoprocessing circuit delivers that channel to a seat display unit (SDU)116 for display.

The microcontroller unit (MCU) board 707 comprises a micro-controller718, an RS-485 port 720 for communication with the DATA 1 bus, anaddress assignment relay 721, and a DPCU interface 722 for communicationwith the digital passenger control units (DPCUs) 134. Themicro-controller 718 receives and transmits communication data on theDATA 1 bus via the RS-485 port 720, provides serial communications tothe digital passenger control units (DPCUs) 134 via the DPCU interface722, and controls the internal operations (i.e. channel selection by theIVAS gate array 706 and video processing circuits 714) of the seatelectronics box (SEB) 130 via an internal bus 724. In a preferred form,the micro-controller 718 comprises an eight (8) bit controller having512 bytes of static RAM and an internal analog-to-digital converter (notshown).

In a particularly innovative aspect of the present invention, themicrocontroller 718 of one seat electronics box (SEB) 130 may beconfigured to communicate with the microcontroller 718 of another seatelectronics box (SEB) 130 via the DATA 1 bus. This enables a digitalpassenger control unit (DPCU) 134 disposed at a first seat location toprovide video channel selection data through a first seat electronicsbox (SEB) servicing that seat location to a second seat electronics box(SEB) 130 servicing a seat location one row forward of the first seatlocation. Thus, a seat display unit (SDU) 116, which receives selectedvideo signals from the second seat electronics box (SEB) 130 and ismounted in the back of the forward seat, may be controlled using thedigital passenger control unit (DPCU) 134 disposed at the rearward seatwithout providing an additional communications link between the twoseats.

IVAS Gate Array Structure and Function

The structure and function of the integrated video audio system (IVAS)gate arrays 310, 410, and 706 shall be explained with reference to FIGS.10-12. However, it should be understood that the structure of theintegrated video audio system (IVAS) gate arrays 310, 410, and 706 doesnot vary throughout the passenger entertainment system 100; only thefunction of the integrated video audio system (IVAS) gate arrays 310,410, and 706 is varied. Moreover, an integrated video audio system(IVAS) gate arrays 310, 410, or 706 comprises a single chip whichfunctions in a different manner depending upon where it is disposedwithin the passenger entertainment system 100. Thus, in a preferred formthe same IVAS gate array chip may be used in the video system controlunit (VSCU) 120, the passenger entertainment system controller (PESC),or any of the seat electronics boxes (SEBs) 130. The function of thechip will vary, however, depending upon where it is disposed.

Referring first to FIG. 10, each IVAS gate array 310, 410, or 706comprises nine (9) functional blocks including a plurality ofpre-scalers 802, a test tone generator 804, a Manchester decoder 806, aaudio formatter 808, an audio buffer 810, timing and control logic 812,a communications controller 814, a PSS/CPMS buffer 816, and a Manchesterencoder 818.

The pre-scalers 802 comprise one portion of a phase lock loop circuit(not shown) and divide down by a programmable factor the frequency of aplurality of signals delivered to their inputs (not shown). The phaselock loop circuit comprises a phase detector, filter circuitry, and avoltage controlled oscillator (VCO) (none of which are shown), eachdisposed externally of the IVAS gate array, and the pre-scalers 802disposed within the IVAS gate array. Each phase lock loop generates aclock phase locked to the PCM data signal. The clock frequencies areprogrammable multiples or sub-multiples of a clock derived from the bitrate (i.e. the data transfer rate) and are provided to the ADPCM gatearrays 306, 318, 406, 418, and 708 and the MASH analog-to-digital anddigital-to-analog converters 302, 320, 404,416, and 710. In thisfashion, sync is maintained throughout the passenger entertainmentsystem 100 based on the frame transfer rate of 37.8 kHz.

The Manchester decoder 806 receives clock and serial audio data inManchester code from a baseband receiver interface 820. The Manchesterdecoder 806 decodes the received serial audio data into NRZ (non-returnto zero) and detects a unique data pattern used for systemsynchronization. Upon detecting the synchronization signal a pulse isgenerated by the Manchester decoder 806 and passed to the timing andcontrol logic block 812. In addition, the NRZ serial audio data isdelivered from the Manchester decoder 806 to the audio buffer 810, theManchester encoder 818, and the CPMS buffer 816.

The test tone generator 804, which comprises a shift register, acounter, and a control logic (not shown), is used for testing signaldistribution within the passenger entertainment system 100. Morespecifically, the test tone generator 804 is capable of generating asquare wave having a programmable frequency and providing that squarewave to one input of a MASH analog-to-digital converter (not shown)disposed within the passenger entertainment system control (PESC) 122.The MASH analog-to-digital converter converts the square wave to adigital format and passes the converted digital signal to an ADPCM gatearray 410 as set forth above. The ADPCM gate array 410 compresses theconverted digital signal and provides the resulting compressed signal toone input of the IVAS gate array 410, where it is multiplexed into thecompressed PCM data signal and distributed throughout the passengerentertainment system 100. Test tone detection circuits (not shown)disposed in the seat electronics boxes (SEBs) 130 detect the presence orabsence of the test tone within the PCM data signal and provide anindication of the existence or non-existence of the test tone to thepassenger entertainment system controller (PESC) 122.

The audio formatter 808 comprises nine 32-bit audio sample shiftregisters (one shift register per eight audio input channels) and a64-bit RF sample shift register (none of which are shown). The primaryfunction of the audio formatter 808 is to insert bit stream datareceived from the compressed digital audio signal sources 102 and theADPCM gate arrays 306, 406, and 418 into the composite PCM data signal.More specifically, the audio formatter 808, under control of the timingand control logic block 812, inserts audio, range, and filter data intothe composite PCM data signal in the frame format illustrated in FIG.11. A fixed relationship is provided between each input port 820 of theaudio formatter 808 and the time slots into which audio and control dataare inserted.

As shown in FIG. 11, each frame 902 of the composite PCM data signalcomprises eight (8) sync bits 904, sixty-four (64) cabin passengermanagement system (CPMS) data bits 906, thirty-two (32) range and filterfactor (R/F) bits 908, six (6) channels comprising twenty-four (24) bitsof passenger address (PA) audio 910, twenty-four (24) channelscomprising ninety-six (96) bits of passenger entertainment systemcontroller (PESC) audio 912, twenty-four (24) channels comprisingninety-six (96) bits of video system controller unit (VSCU) digitalaudio 914, twenty-four (24) channels comprising ninety-six (96) bits ofvideo system controller unit (VSCU) analog audio 916, and twenty-four(24) channels comprising ninety-six (96) bits of video system controllerunit (VSCU) optional digital or analog audio 918. The term "analog," asused in the preceding sentence, denotes that a particular signal wasoriginally generated by an analog audio source. Accordingly, in apreferred form a maximum of 512 bits are provide per frame 902. Itshould be noted, however, that the frame format may be variedsubstantially depending upon the number data types and number of bitsper data type which are to be carried over the signal distributionnetwork. Moreover, it is also preferred that the frame format of theIVAS gate array be programmably variable, such that it may be altered toaccommodate the needs of a given passenger entertainment system oraircraft environment.

Turning now also to FIGS. 12(a) and 12(b) and TABLE 2, those skilled inthe art will appreciate that, when digital data is compressed usingadaptive delta pulse code modulation to the CD-I, level B format, thedata is not merely compressed from a 16-bit format to a 4-bit format.Additional range and filter factors 908 are added to the data. Thesefactors, thus, become an essential component of the composite PCM datasignal and present difficult problem in the context of frame formatting.More specifically, ADPCM compression produces one 4-bit range factor andone 4-bit filter factor for each channel in a twenty-eight frame audiosample. Thus, if 102 channels of ADPCM compressed digital audio (six PAchannels, twenty-four PESC audio channels, and seventy-two VSCU audiochannels) are to be distributed throughout a passenger entertainmentsystem 100, a 4-bit range factor and a 4-bit filter factor must beprovided for each of those 102 channels every twenty-eight frames. In aworst case scenario, transmission of the range and filter (R/F) factorscould require that a 816-bit data block be dedicated solely to range andfilter factors and accompany each frame of compressed digital audio. Incontrast, when a frame format in accordance with the present inventionis utilized, only 32-bits are provided per frame to accommodate therange and filter (R/F) factors. This substantial reduction in the numberof bits per frame needed to accommodate the range and filter factors isaccomplished by staggering the range and filter factors over a number offrames as indicated in TABLE 2.

                  TABLE 2                                                         ______________________________________                                        AUDIO BLOCK TRANSMISSION FORMAT                                               COAX   AUDIO      RANGE/FILTER  SAMPLE NO. 1                                  FRAME  SYNC       CHANNEL NO.s  CHANNEL NO.s                                  ______________________________________                                         1     1          --                                                           2     0          PA1-4         PA1-PA6                                        3     0          PA5-6                                                        4     0          1-4           1-8                                            5     0          5-8                                                          6     0           9-12          9-16                                          7     0          13-16                                                        8     0          17-20         17-24                                          9     0          21-24                                                       10     0          25-28         25-32                                         11     0          29-32                                                       12     0          33-36         33-40                                         13     0          37-40                                                       14     0          41-44         41-48                                         15     0          45-48                                                       16     0          49-52         49-56                                         17     0          53-56                                                       18     0          57-60         57-64                                         19     0          61-64                                                       20     0          65-68         65-72                                         21     0          69-72                                                       22     0          73-76         73-80                                         23     0          77-80                                                       24     0          81-84         81-88                                         25     0          85-88                                                       26     0          89-92         89-96                                         27     0          93-96                                                       28     0          --                                                          29     1          --                                                          30     0          PA1-4         PA1-PA6                                       31     0          PA5-6                                                       32     0          1-4           1-8                                           33     0          5-8                                                         34     0           9-12          9-16                                         35     0          13-16                                                       .      .          .             .                                             .      .          .             .                                             .      .          .             .                                             ______________________________________                                    

More specifically, as shown in FIGS. 11, 12(a) and 12(b) range andfilter (R/F) factors 908 corresponding to only four channels ofcompressed digital audio data are provided in a given frame, and rangeand filter (R/F) factors 908 corresponding to distinct groups of fourchannels each are provided in successive frames. In this fashion, therange and filter (R/F) factors 908 corresponding to all 102 compresseddigital audio channels are provided over the course of a total oftwenty-six frames (e.g. frame Nos. 2-26 as shown in TABLE 2). Further,it is presently preferred to stagger samples of PA and audio data overthe course of twenty-eight frames (i.e. one sample per channel perframe). More specifically, each sample of PA or audio data compriseseight channels (or time slots). Thus, twenty-eight samples of each groupof eight channels (i.e. one sample per frame) are provided within eachblock of PA and audio data. The samples are ordered such that the firstsample (Sample 1) of a given eight channel group falls within the framecontaining the range and filter (R/F) factors 908 corresponding to thefirst channel in the group. For example, the range and filter (R/F)factors 908 corresponding to audio channel No. 1 are placed in frame No.3, and thus, the first sample (Sample No. 1) of audio channel Nos. 1-8is also placed in frame No. 3. Similarly, the range and filter (R/F)factors 908 corresponding to audio channel No. 9 are placed in frame No.5, and thus, the first sample (Sample No. 1) of audio channel Nos. 9-16is also placed in frame No. 5. It will also be noted that it ispresently preferred to place even numbered audio samples in odd numberedframes and odd numbered audio samples in even numbered frames on thecoaxial transmission cable. Turning now also to FIGS. 13(a) and 13(b),the reason for this is that digital audio data, which is received by theaudio formatter 808 during a given frame, is not simultaneouslydelivered to the coaxial downlink (not shown). Instead, digital audiodata received by the audio formatter 808 during one frame is deliveredto the coaxial downlink during the following frame. Further, range andfilter data 908, which is received by the audio formatter 808 during oneframe, is split and delivered to the coaxial downlink over the course ofthe following two frames. When digital audio data is received by theaudio buffer, the digital audio data from a given frame is stored in acurrent data register during that frame and shifted to an outputregister during the next frame. In contrast, range and filter factordata is read and shifted out, as soon as the register assigned theretois filled (i.e. every two frames). For these reasons, it is preferredthat the audio sampling rate of the audio formatter 808 and the audiobuffer 810 be set equal to the frame transfer rate (i.e. equal toapproximately 37.8 kHz), and that synchronization within the passengerentertainment system 100 be maintained based upon the frame transferrate.

It should be understood that it is not intended to limit the presentinvention to the particular frame format depicted in FIG. 11, 12(a),12(b), 13(a) and 13(b), as that format may be varied substantially inaccordance with the present invention. For example, it will be notedthat the composite PCM data signal comprises a plurality of compressionblocks having F frames per block, C digital audio channels per frame,and P compression parameters per channel per block; and any of theseparameters (especially the number of digital audio channels C providedper frame) may be varied. However, in a preferred form the multiplexer14 or IVAS gate array 310 or 410, as the case may be, will be configuredto allocate N time slots per frame for the compression parameters (Nbeing an integer equal to or greater than (CxP)/F) and to assignselected groups of the compression factors (each group comprising N ofsaid compression factors) to selected frames within each compressionblock.

As for the sync signals 904 and 905, a unique audio sync pattern 904(such as that shown in FIG. 11) is provided within the composite PCMdata signal once every twenty-eight frames, and the inverse of thatpattern, the frame sync pattern 905, is provided between all otherframes, as shown in FIGS. 12(a) and 12(b).

Turning again to FIG. 10, the audio buffer 810 comprises four pairs of4-bit shift registers, twelve 8-bit shift registers, and four 16-bitshift registers (none of which are shown). The pairs of 4-bit shiftregisters are used to acquire left and right channel audio samples foreach of up to four passenger seats. When the samples of each pair areacquired, the contents of each pair of shift registers are transferredinto a single 8-bit shift register. The channels are then transferredout of the 8-bit shift register as a single eight bit signal comprisingtwo multiplexed, compressed, digital audio channels. The resultingsignal is then delivered to one input of an ADPCM gate array 706. Theremaining eight 8-bit shift registers are used for acquiring thecompression factors for the left and right channels for each of up tofour passenger seats. When the compression (range and filter) factorsare acquired, they are transferred into the 16-bit shift registers andthen shifted out on the same multiplexed output lines as the compresseddigital audio sample to which they correspond.

Control of the data selection process is provided by the timing andcontrol logic 812, which generates control signals for enabling theshift registers to shift in selected audio channels. More specifically,the timing and control logic 812, in response to signals received from,for example, a digital passenger control unit (DPCU) 134, enables theshift registers to receive data located at a selected channel numbertime slot. A counter, which is reset upon receipt by the timing andcontrol logic 812 of a sync signal, is utilized to provide channelnumber information. Thus, when a channel number selected by the digitalpassenger control unit (DPCU) 134 reaches the timing and control logic812, the data located in the corresponding time slot is passed to theshift registers. Thus, during operation a first shift register of a pairwill acquire an audio data sample from the composite PCM data stream andpass that sample to the second register of the pair. The second shiftregister will then pass the acquired sample to the ADPCM interface, asthe first shift register acquires another sample from the followingframe of the PCM data stream. It may be noted that in the "zero channel"mode described above, a channel number of a non-existent channel isprovided by the digital passenger control unit (DPCU) 134 to the timingand control logic 812. As the timing and control logic 812 neverreceives data corresponding to the channel selected, no new data isentered into the first shift register, and any data previously enteredinto the first shift register will be repeatedly passed on to the secondshift register and eventually to the ADPCM gate array 708.

The timing and control logic 812 controls all timed operations withinthe IVAS gate array 310, 410, and 708. For example, when the IVAS gatearray 310, 410, or 708 acts as a demultiplexer, the control logic 812steers selected audio channels to the audio buffers 810 and divides downthe clock to provide proper timing references for the serial interfaces.The timing and control logic 812 also provides address decoding toenable appropriate registers (not shown) for communication with themicro-controllers 430 or 718 or the central processing unit 316.

The IVCP communications controller 814 manages the communicationprotocol between the IVAS gate array 706 (of the SEB 130) and thein-seat video cassette players (IVCPs) 138.

The PSS/CPMS buffer 816 comprises a 16-bit shift register, a mod 8 bitcounter, a 32 byte FIFO, a status register, a control register, a 16-bitaddress register and control logic (none of which are shown). Thishardware is controlled to operate in one of two different modesdepending upon whether the IVAS gate array is disposed within a seatelectronics box (SEB) 130 or the passenger entertainment systemcontroller (PESC) 122.

When disposed within a seat electronics box (SEB) 130, the PSS/CPMSbuffer 816 is configured to perform a receive function. A start ofmessage byte 920 (shown in FIG. 11) is used to determine the start andend of a message. Each bit in the start of message byte 920 except thefirst bit 921 corresponds to a data byte 924 in the CPMS field 906. Whena start of message bit 922 is high, the channel may be idle or a newmessage may begin in the message byte 924 corresponding to that start ofmessage bit 922. When the start of message bit 922 is low, message datais present. After the message ends, the start of message bit will returnto a high state for the next data byte indicating that the message hasended and that a new message is potentially starting. The control logicalso compares the address field in each message against the address ofthe local unit. An interrupt signal may be provided to themicrocontroller 718 when the addresses are the same.

When disposed within the passenger entertainment system controller(PESC) 122, the PSS/CPMS buffer 816 performs the reverse of the functionperformed in the seat electronics box (SEB) 130. More specifically, thePSS/CPMS buffer 816 will accept messages from the microcontrollerinterface one byte at a time. The bytes are queued up in a FIFO. Thetiming and control logic 812 provides an envelope signalling when thePSS/CPMS buffer may place data into the serial bit stream (PCM datasignal). The queued bytes are strobed into a shift register and shiftedout while the envelope is active. Further, as set forth above, the startof message byte is inserted before the message bytes. The control logicalso makes sure that the first byte of a message is the first byte afterthe start of message byte.

The Manchester encoder 818 encodes the formatted bit stream andgenerates a programmable sync pattern at appropriate times. TheManchester encoder 818 comprises a 16-bit register, a 16-bit shiftregister, a multiplexer, a plurality of gates and a flip-flop (non ofwhich are shown). The register holds the sync pattern loaded by the hostprocessor. During most of a downlink frame, the sync pattern isconstantly loaded into the shift register. When the sync is to betransmitted, the shift register shifts out the sync at twice the bitrate. An XOR gate is used to control the polarity of the sync. Themultiplexer selects between the sync or data based on an externalcontrol signal (sync enable signal provided by the timing and controllogic 812). The flip-flop is used to reclock the edges after encodingthe data.

While the present invention is susceptible to various modifications andalternative forms, specific representations and illustrations thereofhave been shown, by way of example, in the drawings and are hereindescribed in detail. It should be understood, however, that it is notintended to limit the invention to the particular systems and methodsdisclosed, but on the contrary, the invention is to cover allmodifications, equivalents, and alternatives falling within the spiritand scope of the invention as defined by the appended claims.

What is claimed is:
 1. A digital audio distribution system for use onaircraft and other vehicles comprising:a plurality of digital signalsources for generating a plurality of compressed digital audio signaloutputs; a multiplexer having a plurality of signal input terminals forreceiving said compressed digital audio signal outputs, said multiplexerbeing adapted to time domain multiplex said compressed digital audiosignal outputs to produce a single composite data signal; ademultiplexer adapted to receive said composite data signal and toselect a desired channel from said composite data signal; adecompression circuit adapted to receive said selected channel from saiddemultiplexer and to decompress said selected channel to produce adecompressed digital output signal; and a digital-to-analog converteradapted to receive said decompressed digital output signal and toconvert said decompressed digital output signal to an analog audiosignal; whereinsaid composite data signal comprises a plurality ofcompression blocks having F frames per block, C digital audio channelsper frame, and P compression parameters per channel; said multiplexer isconfigured to allocate N time slots per frame for said compressionparameters, N being an integer equal to or greater than (C×P)/F; andsaid multiplexer assigns selected groups comprising N of saidcompression factors to selected frames within each compression block. 2.A method of distributing within an commercial aircraft or otherpassenger vehicle, said method comprising the steps of:generating aplurality of compressed digital audio signal outputs; providing saidplurality of compressed digital audio signal outputs directly to amultiplexer; time domain multiplexing said compressed digital audiosignal outputs to produce a composite digital audio data signal;delivering said composite digital audio data signal to a demultiplexerdisposed at a location remote from said multiplexer; selecting a channelfrom said composite digital audio data signal; decompressing saidselected channel to produce an expanded digital audio signal; convertingsaid expanded digital audio signal to an analog signal; and providingsaid analog audio signal to an audio transducer; whereinsaid compositedigital audio data signal comprises a plurality of compression blockshaving F frames per block, C digital audio channels per frame, and Pcompression parameters per channel; and said time domain multiplexingstep comprises the steps of: allocating N time slots per frame for saidcompression parameters, N being an integer equal to or greater than(CxP)/F; and assigning selected groups comprising N of said compressionfactors to selected frames within each compression block.